Optical absorption spectroscopy is a technique to measure the absorption of light due to the interaction of the light with a target object. For example, light may be transmitted and reflected off of the target object. During this process, some of the light is absorbed by the target object while the remaining light is reflected off of the target object and received by an optical receiver. For instance, in photo-plethysmography (PPG), transmitted light is reflected off the body of a user and received by a light detector. Different levels of blood oxygenation absorb different wavelengths of light. Therefore, the signal that represents the light that is reflected off of and not absorbed by the target object, in this example, the user's body, may be a function of pulsating arterial blood, non-pulsating arterial blood, venous blood, and other tissues. By analyzing the reflected signal, different parameters may be determined. Continuing the PPG example, the heartrate of the user may be determined by analyzing the resulting reflected signal. Unfortunately, in addition to receiving the reflected signal, ambient light may also be received by the optical receiver. Thus, the received signal may contain a component that is a result of the interrogation by the optical system (i.e., the result of the reflected light) and a second component which is a result of the ambient light. Thus, the system must account for the ambient light when analyzing the received signal.